PMN-PT Single Crystals Research Articles

Temperature and pressure effects on elastic properties of lead magnesium niobate-lead titanate relaxorferroelectric material

Lead magnesium niobate—lead titanate (PMN-PT) exhibits exceptional electromechanical properties, considered as a highly efficient transduction material for vibration energy harvesting and acoustic sensing applications. It is reported in the literature that the PMN-PT undergoes structural phase transitions with changes in temperature and the chemical composition. We seek to gain insight into the phase diagram of PMN-PT using temperature and pressure dependence of the elastic properties. Single crystal PMN-PT with chemical composition close to the morphotropic phase boundary (MPB) was used in a resonant ultrasound spectroscopy (RUS) study performed in the temperature range from room temperature to 773 K and the pressure range from near vacuum to 3.4 MPa. At atmospheric pressure, significantly high acoustic attenuation of the PMN-PT material is observed at the temperatures below 400 K. Strong stiffening is observed in the temperature range of 400 K–673 K, followed by a gradual softening at higher temperatures. With the varying pressure, we observed an increased pressure sensitivity of elastic properties of the PMN-PT material that can be localized to the temperature regime where the strong stiffening is observed. As time allows, the behavior of PMN-PT upon cooling below room temperature will also be discussed.

Compositional segregation, structural transformation and property-temperature relationship of high-Curie temperature Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

Ternary ferroelectric single crystal Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) was grown by the modified Bridgman method. The compositional variation of different regions of the crystals was measured, and the segregation regularity of the crystals was proposed. Variations in the dielectric properties and domain structures of the PIN–PMN–PT single crystals were investigated as a function of temperature and composition, and the phase transformation behavior of the crystals was observed. The PIN–PMN–PT crystals showed high Curie temperatures (T C = 160–210 °C), ferroelectric phase transition temperatures (T R–T up to 132 °C) and coercive fields (E C = 6–8 kV/cm) as well as excellent piezoelectric properties (d 33 up to 2,800 pC/N) and electromechanical coefficients (k 33 > 0.90). As the temperature increased, k 33 values remained relatively constant and d 33 increased gradually prior to ferroelectric phase transformation, and these results reflect the wide temperature usage range of PIN–PMN–PT single crystals. The polarization (P r ) and E C of the crystals showed unique trends during the phase transformation process; high P r and E C values can be maintained prior to depolarization, which indicates that the PIN–PMN–PT single crystals are candidate materials for high-power applications. In summary, PIN–PMN–PT single crystals with ultrahigh electric properties, large coercive fields and excellent thermal stability may potentially be applied in harsh environments.

Growth and characterization of high-Curie temperature Pb(Lu1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary single crystal by modified Bridgman technique

A new relaxor-based ferroelectric ternary system Pb(Lu1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PLN–PMN–PT), with a combination of a high-Curie temperature system Pb(Lu1/2Nb1/2)O3–PbTiO3 (PLN–PT) and a high piezoelectricity system Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT), was investigated in this paper. Single crystal PLN–PMN–PT with dimensions of Φ20×45mm3 was grown successfully by the modified Bridgman technique for the first time. The studies of structure and composition of the as-grown crystal showed structural consistency but compositional deviation along the growth direction. The 〈001〉-oriented wafers of the PLN–PMN–PT single crystal showed excellent electrical properties at room temperature: ε33~4500, tanδ~0.5%, d33~2300pC/N. The crystal was found to exhibit high Curie temperature (TC~176°C), rhombohedral–tetragonal phase transition temperature (TRT~108°C) and coercive field (EC~8.1kV/cm), superior to those of PMN–0.3PT single crystal. Studies of temperature dependence ferroelectric properties showed that high values of k33 and d33 could be maintained up to the TRT. These results showed that PLN–PMN–PT piezoelectric single crystal has a higher Curie temperature and coercive field with excellent electrical properties, making the crystal a promising candidate for high-power transducer applications in a broad temperature range.

Deep reactive ion etching of PZT ceramics and PMN-PT single crystals for high frequency ultrasound transducers

Micromachining fabrication technique based on thick photoresist lithography and ICP enhanced deep reactive ion etching of PZT ceramics and PMN-PT single crystals has been investigated to fabricate 1–3 composite piezoelectric materials for high frequency ultrasound transducer applications. The experiment procedure includes thick photoresist patterned lithography, Ni hard mask electroplating and ICP enhanced deep reactive ion etching using chlorine gas. PZT ceramic pillars with a height of 43.78μm and a sidewall angle of 78.9° were obtained. The optimized etching parameters for PZT ceramics were etching rate of 6.25μm/h, and PZT/Ni etching selection ratio of 6.9. PMN-PT single crystal pillars with a height of 30.74μm and a sidewall angle of 84.3° were obtained. The optimized etching parameters for PMN-PT were etching rate of 10.25μm/h and PMN-PT/Ni etching selection ratio of 14. The 1–3 piezoelectric composites fabricated by PZT and PMN-PT pillars are promising materials for fabrication of high frequency ultrasound transducers.

Angled-focused 45 MHz PMN-PT single element transducer for intravascular ultrasound imaging

A transducer with an angled and focused aperture for intravascular ultrasound imaging has been developed. The acoustic stack for the angled-focused transducer was made of PMN-PT single crystal with one matching layer, one protective coating layer, and a highly damped backing layer. It was then press-focused to a desired focal length and inserted into a thin needle housing with an angled tip. A transducer with an angled and unfocused aperture was also made, following the same fabrication procedure, to compare the performance of the two transducers. The focused and unfocused transducers were tested to measure their center frequencies, bandwidths, and spatial resolutions. Lateral resolution of the angled-focused transducer (AFT) improved more than two times compared to that of the angled-unfocused transducer (AUT). A tissue-mimicking phantom in water and a rabbit aorta tissue sample in rabbit blood were scanned using AFT and AUT. Imaging with AFT offered improved contrast, over imaging with AUT, of the tissue-mimicking phantom and the rabbit aorta tissue sample by 23dB and 8dB, respectively. The results show that AFT has strong potential to provide morphological and pathological information of coronary arteries with high resolution and high contrast.

Mechanical confinement for tuning ferroelectric response in PMN-PT single crystal

Ferroelectrics form an important class of materials and are employed for a variety of applications. However, specific applications dictate the need of tailored ferroelectric response. This creates a requirement to obtain ferroelectric materials with tunable properties. Generally, chemical modifications or domain engineering are employed to this effect. This study attempts to shed light on the use of compressive pre-stresses for tuning and enhancing the ferroelectric properties. For the purpose, polarization versus electric field hysteresis data for 68Pb(Mn1/3Nb2/3)O3-32PbTiO3 (PMN-PT) single crystals were obtained as a function of uniaxial compressive stresses and operating temperatures. These data were utilized to investigate the effects of mechanical confinement for four individual case studies of electrocaloric effect, electrical energy storage, pyroelectric, and piezoelectric effect. A significant improvement was obtained for all case studies. The adiabatic temperature change was improved by ≈80% (28 MPa, 353 K); energy storage density increased by a factor of five (28 MPa, 353 K); pyroelectric figure of merits improved by an order of magnitude (21 MPa) and the piezoelectric coefficient was tailored (variable stress). The results offer promising insight into the use of directional confinement for improving application specific ferroelectric properties in PMN-PT single crystal.

High-Curie-temperature relaxor piezoelectric single crystals for 1.5D ultrasound phased-array applications

In this letter, a 2.5MHz 320-element 1.5D active matrix phased-array ultrasound transducer was designed and fabricated using high-temperature relaxor-based piezoelectric ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals. The experiment and finite element analysis with the PZFlex package software were developed to design and optimize the 1.5D transducer. The FEM results show that the −6dB fractional bandwidth is up to 83% using two λ/3.75 matching layers. A 64×5 active element PIN–PMN–PT single-crystal phased array was fabricated and tested. The measured center frequency and −6dB fractional bandwidth were 2.5MHz and 71%, respectively. Elevation beam profiles were obtained using a hydrophone, which showed that the measured −6dB slice thickness was approximately 3mm throughout the entire range of field of interest. The PIN–PMN–PT single crystal with over 30 degree usage temperature and higher Ec field should satisfy the demands of advanced high-density ultrasound transducer applications.

Fundamental understanding of wave generation and reception using d36 type piezoelectric transducers

A new piezoelectric wafer made from a PMN–PT single crystal with dominant piezoelectric coefficient d36 is proposed to generate and detect guided waves on isotropic plates. The in-plane shear coupled with electric field arising from the piezoelectric coefficient is not usually present for conventional piezoelectric wafers, such as lead zirconate titanate (PZT). The direct piezoelectric effect of coefficient d36 indicates that under external in-plane shear stress the charge is induced on a face perpendicular to the poled z-direction. On thin plates, this type of piezoelectric wafer will generate shear horizontal (SH) waves in two orthogonal wave propagation directions as well as two Lamb wave modes in other wave propagation directions. Finite element analyses are employed to explore the wave disturbance in terms of time-varying displacements excited by the d36 wafer in different directions of wave propagation to understand all the guided wave modes accurately. Experiments are conducted to examine the voltage responses received by this type of wafer, and also investigate results of tuning frequency and effects of d31 piezoelectric coefficient, which is intentionally ignored in the finite element analysis. All results demonstrate the main features and utility of proposed d36 piezoelectric wafer for guided wave generation and detection in structural health monitoring.

Bio-inspired bending actuator for controlling conical nose shape using piezoelectric patches.

In this paper, a bio-inspired bending actuator was designed and fabricated using piezoelectric patches and cantilever-shaped beam for controlling nose shape. The aim of this study is to investigate the use of the bending actuator. PZT and single crystal PMN-PT actuators were used to generate translational strain and shear stress. The piezoelectric patches were attached on the clamped cantilever beam to convert their translational strains to bending motion of the beam. First, finite element analysis was performed to identify and to make an accurate estimate of the feasibility on the bending actuation by applying various voltages and frequencies. Based on the results of the FEM analysis, the experiments were also performed. Static voltages and dynamic voltages with various frequencies were applied to the bending actuators with PZTs and PMN-PTs, and the rotation angles of the nose connected to the top of bending actuators were measured, respectively. As the results, the bending actuator using PMN-PT patches showed better performances in all cases. With the increases of signal frequency and input voltage, the rotation angle also found to be increased. Especially at the frequency of 5 Hz and input voltage of 600 V, the nose generated the maximum rotation angle of 3.15 degree.

High temperature resonant ultrasound spectroscopy study on Lead Magnesium Niobate—Lead Titanate (PMN-PT) relaxor ferro-electric material

Lead magnesium niobate-lead titanate [(1-x)PbMg1/3Nb2/3O3-xPbTiO3] is a perovskite relaxor ferroelectric material exhibiting superior electromechanical coupling compared to the conventional piezoelectric materials. In this work, non-poled single crystal PMN-PT material with the composition near morphotropic phase boundary (MPB) was investigated in the temperature range of 400 K—800 K where the material is reported to be in the cubic phase. High temperature resonant ultrasound spectroscopy (HT-RUS) technique was used to probe temperature dependency of elastic constants derived from the measured resonant modes. Non-monotonic resonant frequency trends in the temperature regime indicate stiffening of the material, followed by gradual softening typically observed in heated materials. Elastic constants confirmed this stiffening in the temperature range of 400 K—673 K, where the stiffness constants C11 and C44 increased approximately by 40% and 33% respectively. Acoustic attenuation, derived from the quality factor (Q), exhibits a minimum around the temperature where the stiffness is maximum and, significantly higher attenuation observed at temperatures below 400 K. The temperature range 395 K—405 K was identified as a transition temperature range, where the material showed an abrupt change in the resonant spectrum and, the material emerges from the MPB characterized by this very high acoustic attenuation. This transition temperature compares favorably with dielectric constant measurements reported in the literature.

High pyroelectric power generation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal

We report the pyroelectric power generation of a relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) single crystal. For a temperature variation rate of 0.5 K/s, the PMN–PT generated a closed-circuit current of 10 nA and an open-circuit voltage of 1.1 V at room temperature. The pyroelectric current and voltage of the PMN–PT single crystal were proportional to the temperature variation rate and were sharply enhanced near the structural phase-transition temperature. Additionally, the PMN–PT pyroelectric generator produced stable power for excessive thermal cycling and was highly sensitive to random thermal fluctuations. Our results indicate the potential importance of PMN–PT for high-power pyroelectric generator applications.

Composition dependence of electro-mechanical properties and field induced phase transformations in [001]C PIN–PMN–PT single crystals

The compositional dependence of the electro-mechanical properties of [001]C cut and poled relaxor ferroelectric lead indium niobate—lead magnesium niobate—lead titanate, xPb(In1/2Nb1/2)O3-(1–x−y)Pb(Mg1/3Nb2/3)O3-yPbTiO3 (PIN–PMN–PT) single crystals was characterized under combined stress and electric field loading. Increasing the PIN and PT concentrations in compositions near the morphotropic phase boundary affected the piezoelectric, dielectric, and compliance coefficients, and the ferroelectric, pyroelectric, and thermal expansion coefficients, as well as the ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation thresholds. The combinations of stress and electric field that induced the phase transformations were determined as a function of temperature. The results indicate that the linear response regime can be increased by modifying the composition, but this reduces the piezoelectric, dielectric, and compliance coefficients. This may be a desirable trade off in device design where linearity and low loss are important to the application.

Focused intravascular ultrasonic probe using dimpled transducer elements

High-frequency focused intravascular ultrasonic probes were fabricated in this study using dimple technique based on PMN–PT single crystal and lead-free KNN–KBT–Mn ceramic. The center frequency, bandwidth, and insertion loss of the PMN–PT transducer were 34MHz, 75%, and 22.9dB, respectively. For the lead-free probe, the center frequency, bandwidth, and insertion loss were found to be 40MHz, 72%, and 28.8dB, respectively. The ultrasonic images of wire phantom and vessels with good resolution were obtained to evaluate the transducer performance. The −6dB axial and lateral resolutions of the PMN–PT probe were determined to be 58μm and 131μm, respectively. For the lead-free probe, the axial and lateral resolutions were found to be 44μm and 125μm, respectively. These results suggest that the mechanical dimpling technique has good potential in preparing focused transducers for intravascular ultrasound applications.

Growth and Characterization on PMN-PT-Based Single Crystals

Lead magnesium niobate—lead titanate (PMN-PT) single crystals have been successfully commercialized in medical ultrasound imaging. The superior properties of PMN-PT crystals over the legacy piezoelectric ceramics lead zirconate titanate (PZT) enabled ultrasound transducers with enhanced imaging (broad bandwidth and improved sensitivity). To obtain high quality and relatively low cost single crystals for commercial production, PMN-PT single crystals were grown with modified Bridgman method, by which crystals were grown directly from stoichiometric melt without flux. For ultrasound imaging application, [001] crystal growth is essential to provide uniform composition and property within a crystal plate, which is critical for transducer performance. In addition, improvement in crystal growth technique is under development with the goals of improving the composition homogeneity along crystal growth direction and reducing unit cost of crystals. In recent years, PIN-PMN-PT single crystals have been developed with higher de-poling temperature and coercive field to provide improved thermal and electrical stability for transducer application.

PMN-PT single-crystal high-frequency kerfless phased array.

This paper reports the design, fabrication, and characterization of a miniature high-frequency kerfless phased array prepared from a PMN-PT single crystal for forward-looking intravascular or endoscopic imaging applications. After lapping down to around 40 μm, the PMN-PT material was utilized to fabricate 32-element kerfless phased arrays using micromachining techniques. The aperture size of the active area was only 1.0 × 1.0 mm. The measured results showed that the array had a center frequency of 40 MHz, a bandwidth of 34% at -6 dB with a polymer matching layer, and an insertion loss of 20 dB at the center frequency. Phantom images were acquired and compared with simulated images. The results suggest that the feasibility of developing a phased array mounted at the tip of a forward-looking intravascular catheter or endoscope. The fabricated array exhibits much higher sensitivity than PZT ceramic-based arrays and demonstrates that PMN-PT is well suited for this application.

Magnetoelectric effect in FeCo/PMN-PT/FeCo trilayers prepared by electroless deposition of FeCo on PMN-PT crystals with various orientations

The magnetoelectric (ME) effect was studied in the FeCo/PMN-PT/FeCo trilayer composites prepared by electroless deposition of the FeCo layers on the single crystal PMN-PT substrates with various crystal cuts. X-ray diffraction reveals that the orientation of PMN-PT substrate has no effect on the growth of FeCo layer. The structures with PMN-PT crystals of various orientations have different acoustic resonance frequencies. FeCo/PMN-PT/FeCo composites with PMN-PT of 〈001〉L×〈01‾1〉W×〈011〉T crystal cut shows superior ME performance, which is due to the highest piezoelectric module of PMN-PT.

Super wideband quantitative ultrasound imaging for trabecular bone with novel wideband single crystal transducer and frequency sweep measurement

Current quantitative ultrasound (QUS) imaging technology for bone provides a unique method for evaluating both bone strength and density. The broadband ultrasound attenuation (BUA) has been widely accepted as a strong indicator for bone health status. Researchers have reported BUA data between 0.3 and 0.7 MHz have strong correlation with the bone density. Recently, a novel spiral-wrapped wideband ultrasound transducer fabricated from piezoelectric PMN-PT single crystal is developed by TRS. This novel transducer combines the piezoelectric single crystal material and use of wide-band resonance transducer to provide a bandwidth superior to commercial devices with the capacity for a high sensitivity. To evaluate its application in bone imaging, a trabecular bone plate (6.5 mm thick) was prepared. The TRS transducer emits customized chirp pulses through the bone plate. The bandwidth of the ultrasound pulses is 0.2 MHz, ranging from 0.2 to 3 MHz. Based on the attenuation of the received pulses, the frequency spectrum is created to analyze the attenuation characteristics of the ultrasound attenuation across the super wide bandwidth. This new transducer technology provides more information across a wider bandwidth than the conventional ultrasound transducer and can therefore give rise to new QUS modality to evaluate bone health status.

Influence of TEM specimen preparation on chemical composition of Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

The influences of different transmission electron microscopy (TEM) specimen preparation techniques on the chemical composition of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystals was studied. Ion-milled samples where no cooling with liquid nitrogen (L-N2) was applied show permanently changed composition also deep inside the bulk material. When the PMN–PT samples were cooled to L-N2 temperature during the ion-milling process and in addition lower accelerating voltages were used, the chemical composition was altered only in the thinnest parts close to the specimen edge. Samples prepared using only tripod polishing technique show compositional irregularities close to the specimen edge. For the preparation of lead-containing samples, such as PMN–PT single crystals, a combination of tripod polishing and short Ar-ion-milling at low accelerating voltages while cooling the samples to liquid nitrogen temperature proved to be the most suitable to obtain artefact-free electron-transparent TEM lamellae.

Improved thermal stability of [0 0 1]c poled 0.24Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal with manganese doping

The temperature dependence of dielectric, piezoelectric, and electromechanical coupling properties of 0.5wt.% manganese-doped and undoped [001]c-poled 0.24Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (0.24PIN–0.47PMN–0.29PT) single crystals has been investigated. Compared to the undoped single crystal, the Mn-doped 0.24PIN–0.47PMN–0.29PT demonstrated higher level of coercive field (9.8kV/cm), increased Curie temperature (187°C), improved mechanical quality factor Qm (196), decreased piezoelectric constant d33 and comparable electromechanical coupling factor k33, indicating hardening effects caused by the manganese ion substitution. More importantly, it was found that the Mn substitution significantly enhanced temperature stabilities of k33, d33 and Qm, leading to 30–40°C improvement of the usage temperature range. These results show the application potential of Mn-doped ternary PIN–PMN–PT single crystals for the high-temperature and high-power electromechanical devices.

Minimization of pyroelectric effects in relaxor-PbTiO3 crystals for piezoelectric sensors

To minimize pyroelectric effects while keeping high piezoelectric effects in relaxor-PbTiO3 single crystals, the crystallographic orientation dependence of the pyroelectric and piezoelectric coefficients were investigated for binary (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT), ternary (1 − x − y)Pb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–xPbTiO3 (PIN–PMN–PT) and Mn-doped PIN–PMN–PT single crystals with the “4R” multidomain state. The secondary pyroelectric coefficients were calculated from the thermodynamic inter-relationship between the piezoelectric, elastic, and thermal expansion coefficients, being on the order of (1.16–1.23) × 10−4 C m−2 K−1 for binary crystals and (0.97–2.03) × 10−4 C m−2 K−1 for ternary ones. The primary pyroelectric coefficients were –(6.73–6.84) × 10−4 C m−2 K−1 and −(5.44–6.43) × 10−4 C m−2 K−1 for binary and ternary crystals, respectively. The pyroelectric coefficients could be reduced by matrix rotation, but at the cost of decreasing longitudinal piezoelectric coefficients d33. Of particular interest is that the maximum piezoelectric coefficients d24∗ at θ = ±55o and d34∗ at θ = ±35o by a counterclockwise rotation of θ about the X axis (θ is the rotation angle about the coordinate axes), or d15∗ at θ = ±55o, and d35∗ at θ = ±35o by a counterclockwise rotation the Y axis, were found on the order of 3000 pC N−1. The corresponding pyroelectric coefficients could be reduced by ∼20%. The reduced pyroelectric coefficients that can contribute to decrease undesirable output signals, together with the high piezoelectric coefficients, enable relaxor-PT crystals as favorable candidates for high-sensitivity piezoelectric sensors.